Linked Genes for Calmodulin and E2 Ubiquitin-Conjugating Enzyme in Trichomonas vaginalis

ABSTRACT In searching the genomes of early-diverging protists to study whether the possession of calmodulin is ancestral to all eukaryotes, the gene for calmodulin was identified in Trichomonas vaginalis. This flagellate is a member of the Parabasalia, one of the earliest lineages of recognized eukaryotes to have diverged. This sequence was used to isolate a homologous 1.250-kb fragment from the T. vaginalis genome by inverse polymerase chain reaction. This fragment was also completely sequenced and shown to contain the 3' end of the single-copy calmodulin gene and the 3' end of a gene encoding a protein with high similarity to E2 ubiquitin-conjugating enzymes, a family which has previously only been identified in animals, plants, and fungi. Phylogenetic analysis of 50 members of the E2 family distinguishes at least nine separate subfamilies one of which includes the T. vaginalis E2-homologue and an uncharacterized gene from yeast chromosome XII.     

Caterpillars escape predation in habitat and thermal refuges

1. Climate and, therefore, abiotic conditions, are changing rapidly, and many ecological interactions depend on them. In this study, how abiotic conditions mediate a predator–prey interaction were examined. 2. Caterpillars of Platyprepia virginalis (Boisduval) (Arctiidae) were found previously to be more abundant in wet habitats and thick litter cover compared with drier habitats and little or no litter. We hypothesised that wet litter provided caterpillars with refuges from an important ant predator, Formica lasioides. It was further hypothesised that caterpillars would be able to move at lower temperatures than ants, thus providing them with a thermal refuge. 3. In the lab, caterpillars were more likely to escape ant predation and survive on wet litter and at lower temperatures. At all temperatures, ant recruitment was lower in wet litter than dry litter although ants were more active on litter than bare soil. Thus, wet litter may serve as a habitat refuge for caterpillars from ants. 4. Caterpillars were able to maintain activity at temperatures 8–14 °C lower than F. lasioides. Thus colder temperatures may serve as a thermal refuge for caterpillars from ants. 5. It was hypothesised that caterpillars can escape ant predation when precipitation causes wet litter and at temperatures that they experience commonly in the field. This mismatch between caterpillars and their predators in ability to tolerate wet litter and low temperatures may affect their field distribution and abundance. Expected future warmer and drier conditions may not provide these refuges.     

Metal cation binding by the hyperthermophilic microorganism,Archaea Methanocaldococcus Jannaschii,and its effects on silicification

Abstract: A series of experiments was conducted to determine the capacity of an archaeal strain, Methanocaldococcus jannaschii, to bind metals and to study the effects of metal binding on the subsequent silicification of the microorganisms. The results showed that M. jannaschii can rapidly bind several metal cations (Fe³⁺, Ca²⁺, Pb²⁺, Zn²⁺, Cu²⁺). Considering the lack of silicification of this strain without metal binding, these experiments demonstrate that Fe(III) ion binding to the cell wall components was of fundamental importance for successful silicification and, especially, for the excellent preservation of the cell wall. This study brings new elements to the understanding of fossilization processes, showing that the positive effect of Fe(III) on silicification, already known for Bacteria, can also apply to Archaea and that this preliminary binding can be decisive for the subsequent fossilization of these organisms. Knowledge of these mechanisms can be helpful for the search and the identification of microfossils in both terrestrial and extraterrestrials rocks, and in particular on Mars.     

Cellular Structures, Plasma Membrane Surface Areas and Plasmodesmatal Frequencies of the Stem of Phaseolus vulgaris L. in Relation to Radial Photosynthate Transfer

At an early stage of secondary development, the metaphloem sieveelements appeared to be the only functional axial transportconduit in fully elongated stems of P. vulgaris plants. Thereis no apparent barrier to the radial transfer of solutes inthe stem apoplast. However, radial transfer through the stemsymplast could be limited by discontinuities resulting fromprotoplast degeneration of the protophloem fibres and developingsecondary xylem fibres. Estimates of possible sucrose fluxesthrough the apoplastic and symplastic routes indicated thatradial photosynthate transfer from the sieve element-companioncell (se-cc) complexes of the stem metaphloem could follow eithercellular route. In the case of apoplastic transfer, the plasmamembrane surface area of the se-cc complexes is only sufficientto support some form of facilitated movement of sucrose. Incontrast, the plasma membrane surface area of the phloem parenchymais sufficient to permit passive diffusion of sucrose to theapoplast. Plasmodesmatal frequencies suggest that any symplastictransfer to the phloem parenchyma from the sieve elements wouldbe via the companion cells. Phaseolus vulgaris, french bean, stem, photosynthate, radial transfer (photosynthates), cellular pathway     

NEUROPEPTIDE Y RECEPTORS FROM CALF BRAIN: EFFECT OF CRUDE CONUS VENOM PREPARATIONS ON [H]NPY BINDING

NPY receptors are identified in calf frontal cortex and hippocampus membrane preparations by binding of N-[propionyl-³H] neuropeptide Y. Saturation and competition binding data with PYY, NPY-(18–36) and NPY itself fit with a single class of sites: for the radioligand K_D = 1.4 ± 0.5 nM, B_max = 434 ± 180 fmol/mg protein in frontal cortex, K_D = 0.7 ± 0.2 nM, B_max = 267 ± 50 fmol/mg protein in hippocampus. Competition curves of the Y₁-subtype selective agonist [Leu³¹, Pro³⁴]NPY are biphasic in both membrane preparations: high affinity sites (i.e. Y₁-subtype) amount to 80% in frontal cortex and 23% in hippocampus. The remaining sites are of the Y₂-subtype. Out of 23 Conus venom preparations, 17 inhibit the binding of [³H]NPY in both membrane preparations, but only two of them (from Conus aulicus and C. pennaceus) do so with high potency (ic₅₀ < 5 μg protein/ml). Only one venom preparation (from C. mercator) had weak discriminatory properties (ic₅₀Y₂/ic₅₀Y₁ = 6). Venom from C. anemone increased the [³H]NPY binding 5-fold and with an ic₅₀ of 15–18 μg protein/ml. This binding occurred to the venom itself and was unrelated to the NPY receptors since it was equally potent when displaced by [Leu³¹, Pro³⁴]NPY, NPY-(18–36), PYY and NPY. Copyright © 1996 Elsevier Science Ltd     

Locomotion in Nebalia bipes: a possible model for Palaeozoic phyllocarid crustaceans

The morphofunctional aspects of locomotion in Recent phyllocarid crustaceans are presented, based on combined video observations of living specimens of the cosmopolitan nektobenthic Nebalia (Leptostraca, Nebaliidae) and scanning electron microscopy of fixed material. N. bipes is infaunal by day, showing a preference for organic-rich black muds and dim light conditions. Under natural conditions, emergence from sediment and nocturnal swimming activities are controlled by a circadian rhythm. The 1st and 2nd antennae perform the major role in digging. The carapace rostral plate acts as a ram diverting particles and preventing inputs of sediment into the carapace. Superficial burrowing may provide camouflaged shelter against predation. Swimming is accomplished by the combined action of the first four pairs of pleopods (backward metachronal flexion during the power stroke) and the well-articulated abdominal shaft (downward flap). Plumose setae present on both the pleopods and furcal rami (governed by low Reynolds numbers) behave like paddles maximizing the resistance to the water. Clusters of cuticular microscales (3-5 μm) and microdenticles are present on the external surface of the carapace and the trunk segments, respectively. Both show a uniform directional arrangement suggesting functional interpretations in relation to locomotion (e.g., to prevent back slippage during digging, to reduce turbulence in the flow layer close to the body, and/or to serve as mechanoreceptors for the detection of variation in water flow). Key features of functional importance in the locomotion of living leptostracans (natatory pleopods, a highly flexible abdomen, setulate or paddle-like furcal rami) are also recognized in Palaeozoic archaeostracan phyllocarids, suggesting that swimming was accomplished by the same pleopodal movements as described for N. bipes. Comparisons with Recent analogues (Nebaliopsis) suggest that phyllocarids with a free swimming life-style existed among the lower Palaeozoic archaeostracans (e.g., Caryocaris; Ordovician). Asymmetrical cuticular ornament in some archaeostracans indicates burrowing habits. Some Palaeozoic phyllocarids may have been occasional (possibly diurnal) mud dwellers comparable to modern nebaliids.     

The use of eddy covariance to infer the net carbon dioxide uptake of Brazilian rain forest

• 1 Eddy covariance measurements of CO₂ flux, based on four and six week campaigns in Rondôdnia, Brazil, have been used in conjunction with a model to scale up data to a whole year, and thus estimate the carbon balance of the tropical forest ecosystem, and the changes in carbon balance expected from small interannual variations in climatological conditions.
• 2 One possible source of error in this estimation arises from the difficulty in measuring fluxes under stably stratified meteorological conditions, such as occur frequently at night. Flux may be ‘lost’ because of low velocity advection, caused by nocturnal radiative cooling at sites on raised ground. Such effects may be detected by plotting the net ecosystem flux of CO₂, F_eco is a function of wind speed. If flux is ‘lost’ then F_eco is expected to decline with wind speed. In the present data set, this did not occur, and F_eco was similar to the nocturnal flux estimated independently from chamber measurements.
• 3 The model suggests that in 1992/3, the Gross Primary Productivity (GPP) was 203.3 mol C m^?2 y^?1 and ecosystem respiration was 194.8 mol C m^?2 y^?1, giving an ecosystem carbon balance of 8.5 mol C m^?2 y^?1, equivalent to a sink of 1.0 ton C ha^?1 y^?1. However, the sign and magnitude of this figure is very sensitive to temperature, because of the strong influence of temperature on respiration.
• 4 The model also suggests that the effect of temperature on the net carbon balance is strongly dependent on the partial pressure of CO₂.

     

Natural 15N abundance of vegetation and soil in the Kapalga savanna,Australia

Abstract The natural abundance of the stable isotope ¹⁵N was measured in different vegetation components and in the soil of a northern Australian savanna. Most of the vegetation was found to be ¹⁵N-depleted compared to atmospheric N₂. Herbaceous legumes, perennial grasses, tree legumes, non-legume trees and annual grasses exhibited mean δ¹⁵N of ? 1.7, ? 0.8, ? 0.7, 0.0 and + 0.3‰, respectively. These results are in good agreement with previous studies. Legumes exhibit slightly negative values, indicating that they are likely to be nitrogen-fixing plants. Non-legume plants have a δ¹⁵N close to zero, which could equally result from non-symbiotic fixation, soil organic matter mineralization, or fresh root litter mineralization. In contrast, soil organic matter was ¹⁵N-enriched. Values of δ¹⁵N increased with depth and were + 2.5, + 5.2 and +6.1‰ in the 0–10, 10–20 and 20–40cm layers, respectively. Soil organic matter δ¹⁵N shows a typical profile of mature soils.